Solution-Processed Thick Hole-Transport Layer for Reliable Quantum-Dot Light-Emitting Diodes Based on an Alternatingly Doped Structure.

The operating lifetime of quantum-dot light-emitting diodes (QLED) is a bottleneck for commercial display applications. To enhance the operational stability of QLEDs, we developed a robust solution-processed highly conductive hole-transport-layer (HTL) structure, which enables a thick HTL structure to mitigate the electric field. An alternating doping strategy, which involves multiple alternating stacks of N 4, N 4'-di(naphthalen-1-yl)- N 4, N 4'-bis(4-vinylphenyl)biphenyl-4,4'-diamine and phosphomolybdic acid layers, could provide significantly improved conductivity; more specifically, the 90 nm-thick alternatingly doped HTL exhibited higher conductivity than the 45 nm-thick undoped HTL. Therefore, when applied to a QLED, the increase in the thickness of the alternatingly doped HTL increased device reliability. As a result, the lifetime of the QLED with a thick, alternatingly doped HTL was 48-fold higher than that of the QLED with a thin undoped HTL. This alternating doping strategy provides a new paradigm for increasing the stability of solution-based optoelectronic devices in addition to QLEDs.